Animal cell culture technologies are widely used in biomedical research and pharmaceutical industry. Assessment of cell growth and metabolic activities are essential to the success in the control and improvement of cell culture process. Two of the most commonly monitored metabolites are glucose and lactate. Glucose serves as both a main carbon source and an important energy source in most medium formulation. Entry of glucose into glycolytic pathway leads to the formation of pyruvate as the end product. In animal cells, pyruvate can either be shuttled into the TCA cycle or be converted into lactate. Due to the high flux of glucose to pyruvate and the inefficient coupling between glycolysis and TCA cycle, lactate accumulation tends to occur in continuous cell cultures. Lactate build-up in turn will lead to the acidification of the culture environment. In addition, lactate itself could also be toxic to mammalian cells even under controlled pH. The accumulation of lactate is often a critical limiting factor of a cell culture process especially when the cell density is high.
In biopharmaceutical manufacturing, monitoring glucose and lactate has become a routine practice due to the simplicity and reliability of measurement as well as their chemical stability in culture medium. More importantly, glucose concentration provides an assessment of energy while lactate is considered an important parameter for the accumulation of metabolic byproducts and an indicator of a deteriorating culture environment. As critical culture parameters, glucose and lactate measurements are often the key components in the design for process control in bioreactor operations such as feeding or perfusion strategies.
Significant effort has been made in the past to correlate glucose and lactate metabolism with cell density. The consumption rate of glucose and the accumulation rate of lactate reflect metabolic activities of cultured cells.
As stated earlier accumulation of toxic byproducts such as lactate have an inhibitory effect on cell growth and antibody production. Excessive lactate buildup can result in increased medium osmolarity or, in the absence of pH control, decreased culture pH. The major negative effect of lactate is caused by the decrease in pH that follows from its excretion to the culture medium.
U.S. Pat. No. 6,156,570 teaches process for cultivating cells, preferably mammalian cells, that minimizes the accumulation of lactate.
U.S. Pat. No. 7,429,491 teaches method of improving protein production in animal cell culture using restricted glucose in the fed batch culture.
In the past, attempts have been made to reduce the lactate levels mainly by A] feeding and maintaining a very low level glucose or B] by metabolic engineering of the cells using molecular biology techniques.
This work reveals the correlation between the addition of divalent transitional metal salts (Copper, Zinc) and lactate accumulation and of the possible ways of reducing the same.